Droplet-superfluid compounds in binary bosonic mixtures

TL;DR

This paper investigates a one-dimensional binary bosonic mixture forming a droplet-superfluid compound, revealing complex rotational behaviors and a higher-than-expected superfluid fraction, thus advancing understanding of localization and superfluidity coexistence.

Contribution

It demonstrates the coexistence of superfluidity and localization in a droplet compound with excess atoms, challenging intuitive assumptions about superfluid fractions.

Findings

The compound exhibits simultaneous rigid-body and superfluid behavior.

Residual condensate can carry angular momentum without vorticity.

Superfluid fraction exceeds simple excess atom predictions.

Abstract

While quantum fluctuations in binary mixtures of bosonic atoms with short-range interactions can lead to the formation of a self-bound droplet, for equal intra-component interactions but an unequal number of atoms in the two components, there is an excess part that cannot bind to the droplet. Imposing confinement, as here through periodic boundary conditions in a one-dimensional setting, the droplet becomes amalgamated with a residual condensate. The rotational properties of this compound system reveal simultaneous rigid-body and superfluid behavior in the ground state and uncover that the residual condensate can carry angular momentum even in the absence of vorticity. In contradiction to the intuitive idea that the superfluid fraction of the system would be entirely made up of the excess atoms not bound by the droplet, we find evidence that this fraction is higher than what one would expect in such a picture. Our findings are corroborated by an analysis of the elementary excitations in the system, and shed new light on the coexistence of localization and superfluidity.